Annual rainfall totals in San Diego

Flipping one might be as good a method as any for determining how wet San Diego’s winter will be this year.

What happened to El Niño, the periodic phenomenon that was supposed to appear by summer and increase the odds of a wet year?

“I don’t have much of an answer, to be honest,” said Mike Halpert, deputy director of the Climate Prediction Center in Maryland. “This event has not progressed as we anticipated.”

With El Niño playing hide and seek and the atmosphere providing no other good clues, the experts are basically left to guessing.

Which is what we now ask our readers to do. It’s time for U-T San Diego’s 11th annual Precipitation Prediction Contest. Tell us how much rain you think will fall at Lindbergh Field, San Diego’s official weather station, by the end of the season, which is June 30.

If you nail the number, you can win four two-day, adult lift tickets to Brian Head Ski Resort in Utah, and a two-night stay at the Cedar Breaks Lodge.

Consider whatever predictive factors work best for you: the number of acorns on the oak tree, the width of the caterpillars in the yard, the prognostications in the Farmers’ Almanac, or just plain old intuition. Last year, the winning guess, off by just 0.01 of an inch, came to the winner in a dream.

Send us your entry by midnight Oct. 22. The person who comes closest to the actual total, either over or under, will be the winner. In case of a tie, be sure to include the calendar day that you think will be the wettest.

Before settling on a number, check out the guesses from some pros, and their thinking.

‘Average’ year is a rarity

San Diego’s average annual rainfall is 10.34 inches, but there have been some wild swings in recent years. In 2001-02, the total was 3.02 inches, making it the driest year since 1850, when rainfall records began. In 2004-05, 22.49 inches fell, third most in city history. Two years later, 2006-07 was the fourth driest on record, with only 3.85 inches. Last year, the total was 8.03 inches. So far this season, which began July 1, the total is a trace.

What often (but not always) determines if we end up wet or dry is the El Niño and La Niña cycle. Climatologists closely watch a key region of the equatorial Pacific for clues.

When the sea-surface temperatures stay abnormally high over a multi-month period, El Niño is born. When El Niño is strong, with very high SSTs, we get soaked. If it’s weak, with SSTs just a little above normal, we can end up wet, dry or about normal.

In the spring, the Climate Prediction Center saw warming waters and thought all signs pointed to El Niño’s emergence by July. But now it’s October, and El Niño is still dragging its feet. If it does arrive, it should be on the weak side.